Aid experts are warning that millions of Zimbabwe's people face starvation as the country's political leaders remain deadlocked over a power-sharing deal and the economy heads for total collapse.

While officials of the Southern African Development Community prepare for a meeting tomorrow in Swaziland, where they will try to persuade President Robert Mugabe and opposition leaders to resume negotiations, the UN's World Food Programme (WFP) has warned that the number of Zimbabweans needing food aid is expected to double by early next year to just over five million. The UN has appealed for $140 million (€100m ) to deal with the crisis.

Richard Lee, a WFP spokesman in Johannesburg, said the organisation was already giving emergency food aid to 2.5 million people in Zimbabwe after the failure of the 2008 maize harvest. On top of erratic weather which resulted in droughts in some areas and flooding in others, there were shortages of seed and fertilisers. The government, which buys all grain production, had also failed to set a price that would encourage farmers to grow more than they needed for their own families.

The "worst thing", the WFP official added, was the decision of Mugabe's government to ban all foreign aid work for three months earlier this year, during the violence-wracked second round of the presidential election. The ban was lifted at the end of August.

"This delayed the launch of our programme to feed some 1.7 million people," Lee said. "They were more vulnerable as a result."

The March elections, which saw the ruling Zanu-PF party lose its parliamentary majority and Mugabe trailing his challenger, Morgan Tsvangirai, in the presidential poll, set off a period of turmoil that worsened the plight of rural Zimbabweans. Inflation of 231 million per cent has virtually destroyed the cash economy, and malnutrition, coupled with endemic rates of HIV/Aids, have reduced female life expectancy to 34, the world's lowest. Intimidation of voters and the halt in food aid reduced many rural areas to desperation.

The WFP has described the situation as a "national crisis", with food having run out in some areas. In districts worst affected by drought, including the Zambezi valley and much of Matabeleland and Manicaland, villagers are reported to be surviving on roots and near-inedible wild fruits. Those who have one or two animals are being forced to exchange them for food and basic supplies.

Lee said international donors had been "remarkably generous" with food aid, but Zimbabwe was unlikely to get the development funds it needed until there was evidence that Mugabe was prepared to share power. Hopes were raised by the peace deal signed on 15 September, but all the signs are that Zimbabwe's 84-year-old president is seeking to ignore it. The US is now threatening further sanctions if the agreement collapses.